1. Field of the Invention
The present invention relates to a shell and tube type heat exchanger, a method for catalytic gas phase oxidation that uses the heat exchanger, and a reactor that uses the heat exchanger.
2. Description of the Related Art
In a shell and tube type reactor, a reaction is carried out by charging a heat medium such as molten salt, etc. into a shell chamber having a bundle of reaction tubes therein, circulating the medium, and simultaneously feeding a gaseous raw material for the reaction into the reaction tubes; and the heat generated in the reaction is absorbed by use of the above-mentioned heat medium to thereby maintain the predetermined conditions of a catalytic gas phase oxidation reaction.
Examples of the catalytic gas phase oxidation reaction include reactions producing acrolein from propylene, methacrolein from isobutylene, maleic anhydride frombenzene, phthalic anhydride from xylene and/or naphthalene, acrylic acid from acrolein, and methacrylic acid from methacrolein.
These catalytic gas phase oxidation reactions are accompanied by an extremely large amount of heat, and an abnormal high temperature zone (hot spot) is often locally formed. The reactor might be damaged by thermal strain caused by such heat.
Particularly, in a reactor equipped with a partition sheet that has a plurality of chambers having temperature difference each other, if the temperature difference between the two chambers divided by the partition sheet is great, a big thermal stress is formed in the place. When the temperature difference exceeds a level, the reactor may be broken because of the occurrence of the thermal stress exceeding the maximum allowable stress of the shell. For this reason, in order to decrease the influence on the reactor by heat, an expansion joint that can absorb the distortion that occurs because of the rise or the descent of the temperature of fluid in the shell side is adopted. The joint is formed on the shell of the reactor in the manner in which the inner surface of a long band having a semicircle-like cross section is turned toward the inside of the reactor such that the band makes one round almost horizontally around the shell, and each of the top end and the bottom end of the quasi-semicircle of the long band is connected by use of a known method such as welding to the shell of the reactor which was almost horizontally cut.
However, there remains a drawback in this method that the fluid in the shell side invades the expansion joint to thereby disturb the moving direction of the fluid, and as a result the heat generated in the reaction cannot be sufficiently removed.
Moreover, as one of drawbacks of a catalyst containing molybdenum such as a complex oxide catalyst including molybdenum-bismuth-iron, the molybdenum component sublimes easily when steam exists in the reaction system, and particularly, the sublimation of the molybdenum component is promoted at a high temperature (JP-A-55-113730). In addition, in a reaction accompanied by heat such as the oxidation reaction of propylene, an abnormal high temperature zone (hot spot) is locally formed in the catalytic layer, which raises the conditions where the molybdenum is more easily sublimed as a result. Furthermore, these sublimed molybdenum component is deposited in the part of lower temperature to thereby increase the pressure drop of the catalytic layer. As a result, the hot spot additionally increases. That is, there remains a problem of difficulty in controlling the reaction temperature.
As a consequence, the present invention has been accomplished in view of the foregoing.
Objects of the present invention are to provide a shell and tube type heat exchanger in which the movement of the fluid in the shell side is not disturbed by the expansion joint; a method for the catalytic gas phase oxidation reaction that uses a heat exchanger where the temperature distribution of the fluid in the shell side is uniformed as a whole; and a reactor that uses the heat exchanger.
The object of the present invention is attained by a shell and tube type heat exchanger characterized by attaching an invasion-preventing plate against the fluid in the shell side to the expansion joint portion installed around the periphery of the shell.
Another object of the present invention is attained by a method of the catalytic gas phase oxidation reaction characterized by using the above-mentioned shell and tube type heat exchanger.
The further object of the present invention is attained by a reactor characterized in that the shell and tube type heat exchanger is partitioned into two or more chambers by use of one or more shield sheets transversely of the length of the reaction tube.
According to the present method, it is possible to provide a shell and tube type heat exchanger having a uniformed temperature distribution therein because the fluid in the shell side can be moved, without disturbing by the expansion joint portion, by installing the invasion-preventing plate against the fluid in the shell side.
According to the present invention, it is also possible to uniform the temperature distribution of the fluid in the shell side of a reactor, and extend the lifetime of the whole catalyst because the pressure drop in the reaction tube after the reaction is done for a long term can be uniformized, and at the same time the amount of sublimation of the catalyst constituents such as molybdenum can be uniformized.
According to the present invention, it is possible to provide a reactor having a uniformed temperature distribution in the reactor because the shell of a shell and tube type heat exchanger is partitioned into two or more chambers by use of one or more shield sheets transversely of the length of the reaction tube, and the movement of the fluid in the shell side is not disturbed by the expansion joint portion when different reactions are carried out corresponding to each of the chambers, by installing a invasion-preventing plate against the fluid in the shell side.
The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments.